Multicarrier transmission has been widely adopted in both wired and wireless communication systems such as asymmetric digital subscriber line (ADSL) systems, Digital Video Broadcast (DVB), and wireless local/metropolitan area networks (WLAN/WMAN). Exploiting Discrete Multitone Modulation (DMT) or Orthogonal Frequency Division Multiplexing (OFDM), these systems may achieve greater immunity to multipath fading and impulse noise with lower cost. However, they may also suffer from high peak-to-average power ratios (PAR). Without an appropriate process to counter this problem, the high PAR of a transmitted signal may cause a high-power amplifier (HPA) to operate in its nonlinear region (i.e., the peak-to-peak amplitude of the transmitted signal may be high enough to saturate the amplifier), leading to significant performance degradation.
OFDM effectively partitions overall system bandwidth into a number of orthogonal frequency subchannels. These subchannels are also interchangeably referred to throughout as “tones” or “subcarriers.” In an OFDM system, an input serial data symbol is separated into D groups. Each of the D groups may be mapped onto a quadrature amplitude modulated (QAM) constellation point, and then modulated onto a respective one of N subchannels (or tones) having approximately equal bandwidth and a frequency separation of approximately 1/T, where T is the time duration of an OFDM symbol during which all N groups are transmitted, and D≦N. Generally, the larger the value of D, the larger the system bandwidth, and, because of a resulting quasi-Gaussian distribution in the resulting time-domain signal, the higher the PAR (for example, peak amplitude to average amplitude).
Tone reservation, which modulates reserved or unused ones of the N tones within the signal space to produce data-block-dependent peak-canceling signals, is a technique for reducing the PAR for these systems. That is, where D<N, one may modulate one or more of the unused ones of the N tones to reduce the PAR of the transmitted signal.